The present invention relates to silicone resin compositions and methods for making such compositions. More particularly, the present invention relates to methods for making silicone resins from .beta.-phenylethyltrichlorosilane and an alkylchlorosilane and silicone resin compositions made thereby.
The majority of silicone resins contain both alkyl and phenyl siloxane units. The presence of phenyl siloxane units is particularly important as they convey high heat resistance, oxidation resistance, toughness, air drying ability and compatibility with organic resins to such silicone resins. There are, however, applications for silicone resins that depend not on high heat resistance, oxidation resistance, and the like, but rather upon imparting ultraviolet light resistance and weather resistance to the final product. Most notable of such applications is the copolymerization of the silicone resin with an alkyd or polyester to form a paint vehicle.
Inasmuch as silicone resins containing phenyl siloxane units are relatively expensive, it is desirable to find substitutes therefor and methods for making such substitutes which are more cost efficient but which still provide the properties and characteristics for which the silicone resin was included, i.e. weatherability, UV light resistance, etc.
One substitute for phenyl siloxane units in silicone resins is phenylethylsiloxane units. It is well known that chlorosilanes having at least one silicon-bonded hydrogen atom can be added to styrene to obtain phenylethylchlorosilanes from which resins having phenylethyl siloxane units can be prepared. Generally such addition results in a mixture of various isomers. For example, in the addition reaction of trichlorosilane to styrene using a platinum catalyst some of the silicon-bonded hydrogen atoms of the silane molecules will attach to the carbon atom nearest the benzene ring while some of the silyl radicals of the silane molecules will attach to the carbon atom farthest from the benzene ring, and some of the silicon-bonded hydrogen atoms and silyl radicals will attach in the opposite positions. Accordingly, there results from such addition reaction a mixture of .beta.-phenylethyltrichlorosilane and .alpha.-phenylethyltrichlorosilane. These reactions may be represented by the following equations, respectively: ##STR2##
In the normal course of such addition reaction there is produced a mixture containing approximately 60 weight percent .beta.-phenylethyltrichlorosilane and 40 weight percent .alpha.-phenylethyltrichlorosilane. One disadvantage of such mixture of isomers is that resins made therefrom have a slow rate of reaction with alkyds or polyesters and thus renders it unsuitable as a substitute for phenyl units in paint vehicles and the like.
Brown in U.S. Pat. No. 4,417,069 assigned to the same assignee as the present invention, discloses a novel process for producing .beta.-phenylethylchlorosilane. Briefly, such process comprises forming a mixture of styrene, a chlorosilane having at least one silicon-bonded hydrogen atom, a platinum catalyst and an effective amount of a tertiary amine as a position-directing agent and heating the mixture to effect addition of chlorosilane to the styrene.
Quite surprisingly, the present applicant has discovered that silicone resins formed from substantially 100% .beta.-phenylethyltrichlorosilane and an alkylchlorosilane react with organic compositions, such as alkyds or polyesters much more rapidly than do silicone resins which are formed from mixtures of alpha and beta phenylethyltrichlorosilane and an alkylchlorosilane.
It is therefore an object of the present invention to provide silicone resins comprising .beta.-phenylethylsiloxy units and alkylsiloxy units.
It is also an object of the present invention to provide a method of making silicone resins comprising .beta.-phenylethylsiloxy units and alkylsiloxy units.
It is a further object of the present invention to provide silicone resins suitable for use in formulating paints and varnishes.
It is another object of the present invention to provide silicone resins which exhibit excellent resistance to weather and ultraviolet light.
It is still another object of the present invention to provide a process for producing silicone resins which exhibit increased reactivity with organic compositions.
Other objects and advantages of the present invention will become obvious from the following detailed description.